Welcome to NGA, Pradip!
I don't know how many dogs would like to be active at night, but you might be able to train one to chase squirrels, and then keep leading it your garden at night.
I wonder if a tree can be protected by running chicken wire around the base? Any time I have fought squirrels, they have found a way to go under, over, or through any barrier that I created.
I was picturing myself with a backpack sprayer, chasing my mother around the perimeter of my garden.
But she would have whacked me good if I had ever tried to spray her with any kind of vinegar!
